Magnetic shielding material with insulator-coated ferromagnetic particles

ABSTRACT

A non-conductive magnetic shield material is provided for use in magnetic shields of semiconductor packaging. The material is made magnetic by the incorporation of ferromagnetic particles into a polymer matrix, and is made non-conductive by the provision of an insulating coating on the ferromagnetic particles.

BACKGROUND

Many electronic devices produce electromagnetic radiation (EMR), eitherby design, or as an unintended, or even undesirable byproduct of theirnormal operation. On the other hand, many electronic devices aresensitive to magnetic or electromagnetic radiation, which can, atsufficient strength interfere with operation, corrupt data storage, oractually cause damage. In some cases, for proper operation of a circuitit is preferable, or even necessary to position a device that producesEMR in close proximity to a device that is sensitive to EMR. In othercases, an electronic device that is sensitive to EMR is part of acircuit or product that may be required to operate in environments whereEMR of significant strength is likely to be present. Depending upon thecircumstances, magnetic shielding may be required at any level,including the product level, the inter-circuit level between circuits ona circuit board or between circuit boards, the inter-chip level betweenchips on a circuit board, the package level protecting the one or moreintegrated circuits in a package, and even the inter-circuit levelbetween circuits on a single IC chip.

Ferromagnetic metals and their alloys having high magnetic permeabilityare effective shields for static and low frequency EMR. These caninclude, for example, elemental iron (Fe), mu-metal, and permalloy, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a diagrammatic side-sectional view of a wire-bond-type ICpackage with package-level magnetic shielding.

FIG. 2A is a diagrammatic side-sectional view of a wire-bond-type ICpackage with package-level magnetic shielding, according to anembodiment.

FIG. 2B is an enlarged view of a portion 2B of the package of FIG. 2A.

FIGS. 3-14 show examples of various types of semiconductor packagesemploying non-conductive magnetic shielding material, according torespective embodiments.

FIG. 15 is a flow chart outlining a method for magnetically shielding asemiconductor package 280, according to an embodiment.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

FIG. 1 is a diagrammatic side-sectional view of a wire-bond-type ICpackage 100 with package-level magnetic shielding. The package 100includes an integrated circuit die 102 having contact terminals 103,mounted to a package substrate 104, together with upper and lowermagnetic shield plates 106, 108. Layers of epoxy 110 bond the die 102 tothe lower shield plate 108 and the lower shield plate 108 to the packagesubstrate 104. A layer of magnetic epoxy 112 bonds the top shield plate106 to the die 102 and the lower shield plate 108. A wire-bond window114 extends through the lower shield plate 108 and the package substrate104, and bond wires 116 electrically couple the contact terminals 103 ofthe die 102 to terminals 117 of the package substrate 104. A “glob-top”fill or molding compound 118 encapsulates and protects the bond wires116 from damage. A ball grid array 120 is positioned on the bottom ofthe package substrate 104, and is configured to electrically couple thepackage 100 to a corresponding contact array on a circuit board oranalogous substrate. A magnetic shield 122 is formed by and includes theupper and lower shield plates 106, 108 and the magnetic epoxy 112.

In embodiments in accordance with the present disclosure, the magneticepoxy 112 is a matrix of epoxy material containing ferromagneticparticles. The magnetic epoxy 112, particularly in the regions where itbonds the upper shield plate 106 to the lower shield plate 108,completes the magnetic “circuit” of the shield enclosure formed by theupper and lower shield plates 106, 108, which otherwise would be openaround the entire perimeter.

As magnetic field strength increases, a magnetic shield will tend tobecome saturated, at which point its effectiveness as a shield drops offHigher magnetic permeability materials saturate at higher magnetic fieldstrengths, meaning that, other factors being equal, a shield having ahigher magnetic permeability will protect against higher magnetic fieldstrengths than a lower magnetic permeability shield. Accordingly, themagnetic shield plates 106, 108 and the ferromagnetic particles of themagnetic epoxy 112 will often be made of material with a high magneticpermeability, such as mu-metal, permalloy, elemental iron, soft ironalloy, etc. However, embodiments of the present disclosure are notlimited to materials exhibiting a magnetic permeability falling within aparticular range, inasmuch as an appropriate magnetic permeability, in agiven instance, will depend upon the susceptibility of the device to beprotected from harm due to magnetic fields, as well as the environmentin which the device is to be operated. Accordingly, embodiments areenvisioned in which a relatively low magnetic permeability isacceptable, and others in which a very high magnetic permeability isappropriate. In accordance with other embodiments of the presentdisclosure, ferromagnetic particles not considered to have a highmagnetic permeability are present in the magnetic shield in combinationwith ferromagnetic particles having a different magnetic permeability,e.g., higher magnetic permeability. Embodiments of the presentdisclosure are not limited to the specific ferromagnetic materialsdescribed above. Other materials exhibiting ferromagnetic properties andhigher or lower magnetic permeability may be used in a magnetic shieldin accordance with the present disclosure.

Terms such as conductive and non-conductive, and the like, are usedherein with reference, specifically, to electrical conductivity.

In tests conducted with a structure like that shown in FIG. 1, it wasfound that, in general, the structure was effective in attenuating amagnetic field applied perpendicular to the package substrate 104—i.e.,parallel to the Z axis. However, in the region of the die 102 lyingdirectly over the wire-bond window 114, attenuation of the magneticfield was not as great—e.g., magnetic field strength in that region ofthe die increased by about 400%-600%.

The inventors have recognized that if the fill material of the glob topor molding compound 118 were formulated with ferromagnetic particles,similar to the magnetic epoxy 112, this would eliminate the weak spot inthe magnetic shield protecting the die 102. However, the inventors alsorecognized that this is not practical, because the high particle loadingwould render the fill material conductive, and electrically short thebond wires 116.

As a result, most magnetically shielded semiconductor package designshave vulnerable regions, particularly where electrical connectors areused to electrically couple a semiconductor die to a package element,such as the package substrate 104, in the present example, that providesinput and output connections to the exterior of the package.

Epoxy, per se, is not typically electrically conductive, nor does ithave any magnetic properties that are of particular interest here. Themagnetic epoxy 112 is made magnetically permeable by addition offerromagnetic particles suspended in the epoxy matrix, but thoseparticles also tend to increase conductivity of the epoxy/particlemixture. As noted above, in an application where magnetic shielding isrequired, the particles are preferably highly magnetically permeable.However, the permeability of the magnetic epoxy 112 depends not onlyupon the permeability of the particles, but also on the density of theparticles in the mixture. As the volume ratio of particles to totalvolume (i.e., epoxy matrix+particles) increases, the effectivepermeability of the mixture increases. Thus, a higher particlevolume:mixture volume ratio (hereafter, PMR) is preferable for effectivemagnetic shielding. However, above a threshold PMR, the mixture becomeselectrically conductive. A magnetic material that provides anysignificant magnetic shielding will typically have a PMR above aconduction threshold volume ratio (hereafter, CTR) of the material whichis the PMR at which the material become conductive.

FIG. 2A is a diagrammatic side-sectional view of a wire-bond-type ICpackage 130 with package-level magnetic shielding, according to anembodiment. FIG. 2B is an enlarged view of a portion 2B of the package130 of FIG. 2A. The package 130 is similar in most respects to thepackage 100 of FIG. 1, except that it comprises a magnetic shield 131that includes a glob top closure or molding compound 132 formed with anon-conductive magnetic fill material 134 that contributes to themagnetic shielding of the package provided by the other elements of themagnetic shield, 131, i.e., upper and lower shield plates 106, 108 andmagnetic epoxy 112. In the embodiment of FIG. 2A, the bond wires 116extend through the non-conductive magnetic fill material 134, whichencapsulates and insulates them. In accordance with disclosedembodiments, the PMR falls within a range of between about 10% and about80%. In other embodiments, the PMR falls within a range of between about30% and about 60%. Embodiments of the present disclosure are not limitedto PMRs that fall within the above ranges. In other embodiments inaccordance with the present disclosure, PMR may fall below the lowerends of the above ranges or above the upper ends of the above ranges.

FIG. 2B, which shows an enlarged portion of the wire-bond window 114 andglob-top closure or molding compound 132, shows, in particular, detailsof the non-conductive magnetic fill material 134. The non-conductivemagnetic fill material 134 includes a high percentage of ferromagneticparticles 136, each of which has an insulating coating 138. The coatedferromagnetic particles 136 are suspended in a matrix 140 ofnon-conductive material. The insulating coatings 138 electricallyinsulate the ferromagnetic particles 136 from each other, making themixture non-conductive at a higher PMR than the magnetic epoxy 112,while providing an adequate level of magnetic shielding. This ispossible, in part, because the insulating coating 138 imposes a minimuminsulator thickness between adjacent ferromagnetic particles 136 in themix, as explained in more detail below.

Referring again to the magnetic epoxy 112 of FIG. 1, ferromagneticparticles are suspended in a matrix of non-conductive epoxy material ina substantially random distribution within the matrix, so that the spacebetween some of the particles is many time greater than the spacebetween other particles. Even at a relatively low PMR, there are likelyto be many particles that are in physical contact with each other, witheffectively no insulating material separating them, while otherparticles will be many times farther apart than an overall averageparticle spacing. The PMR primarily defines the average spacing ofparticles in the mixture, not the individual spacing, but the individualspacing is a critical factor of the CTR.

As ferromagnetic particles are added to the matrix of non-conductiveepoxy and the PMR increases, more and more of the ferromagneticparticles are spaced closer and closer together. Eventually, a particledensity is reached—i.e., the CTR—at which it is a near certainty thatthere will be one or more paths, within the aggregate of non-conductiveepoxy and ferromagnetic particles, extending from ferromagnetic particleto ferromagnetic particle through the matrix of non-conductive epoxy, inwhich each pair of adjacent ferromagnetic particles in the path arespaced closely enough to each other that the total thickness ofinsulating material along the path is small enough that an appliedvoltage produces dielectric breakdown, and the path of ferromagneticparticles in the matrix becomes electrically conductive. Nevertheless,at that PMR the ferromagnetic particle spacing along that electricallyconductive path is much lower than the overall average spacing offerromagnetic particles within the aggregate of the non-conductive epoxyand ferromagnetic particles. If, instead, the spacing between everyferromagnetic particle in the matrix of non-conductive epoxy wereconstrained, so that no two ferromagnetic particles could be positionedany closer than some minimum distance, the CTR, i.e., the minimum PMR atwhich the mixture of ferromagnetic particles and non-conductive epoxybegins to conduct, would be much higher.

Turning, now, to the non-conductive magnetic fill material 134 of FIG.2B, the distribution of the ferromagnetic particles 136 in thenon-conducting matrix is random, just as in the magnetic epoxy 112 (FIG.2A). However, in this case, when two of the ferromagnetic particles 136bump into each other, they are still separated by the thicknesses oftheir respective insulating coatings 138. The closest spacing possiblebetween any two of the particles is equal to the sum of the thickness ofthe insulating coating on each of the particles. When the thickness ofthe insulating coating 138 on each of the ferromagnetic particles isequal, the closest spacing possible between any two particles is equalto twice the thickness of the insulating coating 138. This is a minimuminsulator thickness that is imposed by the insulating coatings 138 onthe ferromagnetic particles 136.

Thus, assuming ferromagnetic particles of equal size and composition,the magnetic epoxy 112 of FIG. 1 and the non-conductive magnetic fillmaterial 134 of FIGS. 2A, 2B will have equal permeabilities at equalPMRs. However, other factors being equal, the CTR of the non-conductivemagnetic fill material 134 will be higher than that of the magneticepoxy 112. It should be noted that, for purposes of determining theparticle:mixture ratio of the non-conductive magnetic fill material 134,the insulating coating 138 on the ferromagnetic particles 136 isincluded in the mixture, along with the matrix 140 and the particles.

The size of the ferromagnetic particles 136 can vary, but falls,according to various embodiments, generally in a range of between about0.1 micron to about 100 microns in average diameter. According to anembodiment, an average diameter of the ferromagnetic particles isbetween about 1 and 30 microns. Embodiments in accordance with thepresent disclosure are not limited to ferromagnetic particles havingaverage diameters falling within the above ranges. According to otherembodiments, ferromagnetic particles used in non-conductive magneticfill materials have average diameters less than 0.1 micron or greaterthan 100 microns. In some embodiments, regular, i.e., non-ferromagneticfillers/particles may also be added into the molding compound orunderfill along with the inclusion of ferromagnetic fillers. Theparticle size of ferromagnetic fillers/particles added in the moldingcompound may be different from the size added in the underfill. Forexample, the particle size in the molding compound will be larger, andthe particle size in the underfill may be smaller due to theirfunctionalities. In some embodiments, for the underfill, the particlesize will be about single digit microns, while for the molding compound,the particle size will be about double-digit micron size.

The insulating coating 138 on the ferromagnetic particles 136 can be anyappropriate insulator/dielectric material compatible with the materialof the non-conductive matrix of the non-conductive magnetic fillmaterial 134. For example, according to an embodiment, the insulatingcoating 138 is an electrically non-conductive polymer material that isdeposited via physical or chemical processes/reaction. Examples ofpolymer materials useful as insulating coating 138 include polyethylene,styrene-acrylic, and carboxylated styrene-butadiene. According to afurther embodiment, the insulating coating 138 is an inorganic compound,such as a dielectric oxide, silicon dioxide, for example, or a ceramicmaterial. The material of the matrix can be any appropriate material forthe particular application, including, for example, silicone, epoxy, andother polymers, etc.

The thickness of the insulating coating 138, which controls the minimuminsulator thickness, varies according to ferromagnetic particle size,the dielectric constant of the material of the coating, and a desireddielectric strength of the mixture. It will be understood that if theferromagnetic particles 136 are relatively large, the number offerromagnetic particles required to form a conductive path between twopoints will be fewer than if the ferromagnetic particles are relativelysmaller. With fewer ferromagnetic particles in the path, and assuming atotal value of insulator thickness along the path required to preventconduction is constant, then the average insulator thickness betweeneach adjacent pair of ferromagnetic particles in the path is greater forlarger ferromagnetic particles than for smaller ferromagnetic particles.Similarly, the minimum insulator thickness is also greater for largeparticles than for smaller ones. Thus, the minimum thickness of theinsulating coating and particle size are directly related. Anotherfactor affecting the desired thickness of the insulating coating 138 isthe dielectric constant of the material of the insulating coating 138.High-k dielectrics have a higher breakdown voltage, and can thuswithstand a higher voltage at a given thickness, so a coating of ahigh-k dielectric material can be thinner than a lower k dielectricmaterial, for a given voltage. Thus, the minimum insulator coatingthickness and the dielectric constant of the coating material areinversely related. In accordance with embodiments of the presentdisclosure, the insulating coating 138, has a thickness ranging fromabout 0.01 microns to about 3 microns. In other embodiments, thethickness of the insulating coating 138 falls within a range of about0.05 microns to about 2 microns. In other embodiments, the insulatingcoating 138, has a thickness that is less than the lower end of theranges described above or greater than the upper end of the rangesdescribed above.

The insulator-coated ferromagnetic particle:mixture volume ratio of thenon-conductive fill material 134 is selected to be lower than the CTR ofthe mixture in the intended application, and to have a magneticpermeability that is adequate to provide a desired degree of magneticshielding. It should be noted that the design parameters of the device,which include the spacing of the bond wires 116, the maximum voltagedifferences applied across any two of the wires, etc., will impose aminimum dielectric strength of the mixture necessary to avoid dielectricbreakdown during operation of the device. This, in turn, will impose amaximum PMR value, so the magnetic permeability of the mixture may belimited by the dielectric strength requirements of the device. Theseimposed values can be modified at the design stage, in a number of ways.For example, spacing of the bond wires can be modified, electrical pathsbetween which the highest voltage differences will be applied can beassigned to wires that are farthest apart in the array, the material ofthe insulating coating on the ferromagnetic particles can be selected tohave a higher k value, and the material of the epoxy matrix can beselected to have a higher breakdown voltage.

Referring again to FIG. 2A, according to another embodiment, the uppershield plate 106 is bonded to the die 102 and the lower shield plate 108by a layer of non-conductive epoxy 110, which includes ferromagneticparticles that each have an insulating coating, as described withreference to the non-conductive magnetic fill material 134.

The package 130 described above with reference to FIGS. 2A and 2B isprovided as one example of a device that can benefit from anon-conductive magnetic shield in accordance with embodiments of thepresent disclosure. Other package configurations are contemplated, thatcan also benefit similarly. FIGS. 3-14 are diagrammatic side-sectionalviews of various semiconductor packages, with package-level magneticshielding, according to respective embodiments of the presentdisclosure.

FIG. 3 shows a surface-mount lead-frame package 150, according to anembodiment, in which the semiconductor die 102 is bonded to a lead framepaddle 152 by a layer of epoxy 110. The die 102 is wire bonded tofingers 154 of the lead frame, and the die 102, bond wire 116, andpaddle 152 are encased in a package body 155 of a non-conductivemagnetic molding compound 156. The non-conductive magnetic moldingcompound 156 includes ferromagnetic particles with insulating coatingssubstantially as described with reference to FIG. 2B. The non-conductivemagnetic molding compound 156 acts as a magnetic shield 158, to protectthe die 102 from magnetic interference.

FIG. 4 shows a wire-bond ball-grid-array package 160, according to anembodiment. The die 102 is bonded to a magnetic heat spreader 162 by alayer of epoxy 110. Contacts on the die 102 are electrically coupled toa package substrate 164 via bond wires 116, and thence to a ball gridarray 120 via electrical traces formed in the substrate 164. A packagebody 166 of non-conductive magnetic molding compound 156 encapsulatesthe die 102, heat spreader 162, and wire bonds 116 on the packagesubstrate 164 is and forms, with the magnetic heat spreader, a magneticshield 168.

FIG. 5 shows a wire-bond lead-frame package 170, according to anembodiment, in which the die 102 is mounted to frame fingers 172 bydeposits of adhesives (a layer of epoxy 110). Bond wires 116electrically couple electrical contacts of the die 102 to respectiveframe fingers 172 and the die 102, bond wires 116, and fingers 172 areencapsulated in a package body 174 of non-conductive magnetic moldingcompound 156, that acts as a magnetic shield 158.

FIG. 6 shows a wire-bond ball-grid-array package 180, according to anembodiment, in which the die 102 is bonded to a heat spreader 182, whichis in turn bonded to a package substrate 104 by layers of epoxy 110.Bond wire 116 electrically couples the die 102 to the package substrate104 via a wire-bond window formed in the heat spreader 182 and thepackage substrate 104. A ball grid array 120 is positioned on the bottomface of the package substrate 104. A package body 184 of non-conductivemagnetic molding compound 156 encapsulates the die 102 and heat spreader182 on the package substrate 104. A glob top closure or molding compound132 formed with a non-conductive magnetic fill material 134—which,according to one embodiment, is substantially similar to thenon-conductive magnetic molding compound 156 described above withreference to FIGS. 2A and 2B—protects the bond wires 116. A magneticshield 186 comprises the package body 184, the heat spreaders 182 andthe glob top closure or molding compound 132.

FIG. 7 shows a flip-chip ball-grid-array package 190, according to anembodiment, in which the die 102 is coupled to a package substrate 192via a micro-ball or bump array 194. A ball grid array 120 is positionedon the bottom face of the package substrate 192. A non-conductivemagnetic underfill layer 196 is positioned between the die 102 and thepackage substrate 192, and a package body 198 of non-conductive magneticmolding compound 156 encapsulates the die 102 on the package substrate192. The non-conductive magnetic underfill layer 196 includesferromagnetic particles with insulating coatings substantially asdescribed above with reference to FIG. 2B. A magnetic shield 199 isprovided, which includes the package body 198 and the underfill layer196.

According to an alternative embodiment in accordance with the presentdisclosure, in FIG. 7, the underfill layer 196 is omitted. Duringencapsulation, the non-conductive magnetic molding compound 156 fillsthe gap between the underside of die 102 and the package substrate 192,and forms a part of magnetic shield 199.

In some cases, further magnetic shielding can be employed, in additionto the shielding provided by, for example, a package body of a magneticmolding compound in accordance with embodiments described above. Theembodiments of FIGS. 8-14 provide examples of semiconductor packagesthat employ shield plates and similar structures, formed ofhigh-permeable material similar to the shield plates 106, 108 describedwith reference to FIGS. 1 and 2A.

FIG. 8 shows a flip-chip ball-grid-array package 200, according to anembodiment, in which the die 102 is coupled to a package substrate 192via a micro ball or bump array 194. A heat spreader 202 is coupled tothe upper surface of the die 102 via a thermally conductive grease 204.The heat spreader 202 is formed of a material having a highpermeability, so as to function as part of a magnetic shield 206 thatincludes an underfill layer 196, as well.

FIG. 9 shows a semiconductor package 210, according to an embodiment.The package 210 is similar in most respects to the package 150 of FIG.3, but also includes a package case 212 that comprises upper and lowermagnetic shield plates 214, 216.

FIG. 10 shows a semiconductor package 220, according to an embodiment.The package 220 is similar in most respects to the package 160 of FIG.4, but also includes a package case 222 that comprises an upper magneticshield plate 224. A heat spreader 226 is provided below die 102. Heatspreader 226 is made of a material with a high-permeability, andfunctions as a lower magnetic shield plate.

FIG. 11 shows a semiconductor package 230, according to an embodiment.The package 230 is similar in most respects to the package 170 of FIG.5, but also includes a package case 212 that comprises upper and lowermagnetic shield plates 214, 216.

FIG. 12 shows a semiconductor package 240, according to an embodiment.The package 240 is similar in most respects to the package 180 of FIG.6, but also includes a package case 242 that comprises an upper magneticshield plate 244. A heat spreader 246 is provided below die 102 and ismade of a material with a high-permeability. Heat spreader 246 functionsas a lower magnetic shield plate. The left and right sides of the uppershield plate 244 extend around and over the lower shield plate/heatspreader.

FIG. 13 shows a semiconductor package 250, according to an embodiment.The package 250 is similar in most respects to the package 190 of FIG.7, but also includes a package case 222 that comprises an upper shieldplate 224.

FIG. 14 shows a semiconductor package 260, according to an embodiment.The package 260 is similar in most respects to the package 200 of FIG.8, but in addition to the underfill layer 196, includes a non-conductivemagnetic molding compound 156 that fills the balance of the package 260.

FIG. 15 is a flow chart outlining a method for magnetically shielding asemiconductor package 280, according to an embodiment of the presentdisclosure. At step 282, a non-conductive magnetic mixture is formed, bycombining a plurality of ferromagnetic particles, each having aninsulating coating, with a matrix material, at a volume ratio thatimparts a selected magnetic permeability to the mixture.

At step 284, the mixture is positioned around and between a plurality ofelectrical connectors that electrically couple contact terminals of asemiconductor die with contact terminals of an input/output interface ofthe semiconductor package, and at step 286, the mixture is cured.

According to an embodiment, the mixture is a glob-top fill material ormolding compound that is positioned within a wire-bond window of thepackage, and that protects bond wires that couple contact terminals ofthe semiconductor die with contact terminals of a package substrate.According to another embodiment, the mixture is an underfill material ormolding compound that surrounds and protects a plurality of bumps thatelectrically couple the semiconductor die to a package substrate.According to a further embodiment, the mixture is a molding compoundthat encapsulates the semiconductor die and the electrical connectorsthat couple the die to a lead frame, a package substrate, etc.

The non-conductive magnetic shielding materials described above providea significant advantage over other magnetic materials that cannot beused in contact with electrical conductors. The non-conductive materialscan be used between and around electrical connectors within asemiconductor package, insulating the connectors while magneticallyshielding the semiconductor die(s) within the package. This is incontrast to other known package shielding materials that cannot be usedin contact with electrical connectors, and that therefore cannot be usedto provide magnetic shielding in regions where electrical connectionsare formed between a semiconductor die and an input/output interfaceelement of the package.

Examples of non-conductive magnetic materials are described above inconjunction with various types of semiconductor packages, the materialsincluding epoxy, molding compound, glob-top filler, underfill, etc.These materials are made magnetic by the incorporation of ferromagneticparticles into a polymer matrix, and are made non-conductive by theprovision of an insulating coating on the ferromagnetic particles. Thenon-conductive character of the materials enables their use insemiconductor packages as magnetic shielding material that is inphysical contact with electrical conductors, providing not only magneticshielding, but also electrical insulation.

According to one embodiment, a device includes a magnetic shield thatincludes a plurality of ferromagnetic particles encapsulated in a matrixwith each of the plurality of ferromagnetic particles being encapsulatedby an insulating coating.

According to another embodiment, a device includes a semiconductor diehave a plurality of die terminals and a package input/output interfacehaving a plurality of package input terminals and a plurality of packageoutput terminals. A magnetic shield is positioned to shield thesemiconductor die from magnetic fields and includes a non-conductivemagnetic shield element. The device includes a plurality of electricalconnectors coupling respective die terminals to corresponding packageinput terminals. The electrical connectors extend through and are inphysical contact with the non-conductive magnetic shield element.

According to another embodiment, a method for forming a magnetic shieldis provided. The method includes forming a mixture of ferromagneticparticles having an insulating coating and a matrix material at a volumeratio of particles to mixture that imparts a selected magneticpermeability to the mixture. According to the method, the mixture ispositioned around and between a plurality of electrical connectors thatelectrically couple contact terminals of a semiconductor die withcontact terminals of an input/output interface.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device, comprising: a semiconductor die; amixture on a first portion of the semiconductor die and having: aplurality of first ferromagnetic particles; an insulating coatingencapsulating each of the plurality of ferromagnetic particles; and amatrix containing the first ferromagnetic particles; and a matrix ofepoxy material on a second portion of the semiconductor die and having aplurality of second ferromagnetic particles, wherein the mixture isnon-conductive at a particle volume to mixture volume ratio (PMR)between 10% to 80% and the matrix of epoxy material having a pluralityof second ferromagnetic particles is conductive at a PMR that is lowerthan the PMR at which the mixture is non-conductive.
 2. The device ofclaim 1, wherein the mixture is non-conductive at a PMR between 30% to60%.
 3. The device of claim 1 wherein the matrix containing the firstferromagnetic particles is a silicone or epoxy polymer.
 4. The device ofclaim 1 wherein the matrix containing the first ferromagnetic particlescomprises a glob-top fill.
 5. The device of claim 1 wherein the matrixcontaining the first ferromagnetic particles comprises a die underfill.6. The device of claim 1 wherein the matrix containing the firstferromagnetic particles comprises a semiconductor package moldingcompound.
 7. The device of claim 1 wherein the insulating coatingcomprises a polyethylene, styrene-acrylic or carboxylatedstyrene-butadiene polymer.
 8. The device of claim 1 wherein theinsulating coating comprises a dielectric oxide.
 9. The device of claim1, wherein the matrix of epoxy material is a magnetic epoxy and thedevice further comprises a first shield plate coupled to the magneticepoxy.
 10. The device of claim 9, further comprising a second shieldplate coupled to the magnetic epoxy, wherein the first shield plate isabove the semiconductor die and the second shield plate is below thesemiconductor die.
 11. The device of claim 10, wherein the second shieldplate is in contact with the magnetic epoxy.
 12. A device, comprising: asemiconductor die having a plurality of die terminals; a packageinput/output interface having a plurality of package input terminals anda plurality of package output terminals; a mixture on a first portion ofthe semiconductor die, the mixture including a plurality offerromagnetic particles and a matrix of non-conductive material forminga non-conductive magnetic shield element shielding a first portion ofthe semiconductor die, the non-conductive magnetic shield element havinga ferromagnetic particle volume to mixture volume ratio (PMR) that isless than a conduction threshold volume ratio (CTR) of thenon-conductive magnetic shield element; a conductive magnetic shieldelement shielding a second portion of the semiconductor die; and aplurality of electrical connectors electrically coupling respective dieterminals to corresponding package input terminals, each of theelectrical connectors extending through and in physical contact with thenon-conductive magnetic shield element.
 13. The device of claim 12wherein the plurality of ferromagnetic particles of the non-conductivemagnetic shield element include an insulating coating encapsulating eachof the plurality of ferromagnetic particles
 14. The device of claim 13wherein the insulating coating is a ceramic material.
 15. The device ofclaim 12 wherein the matrix is a polymer.
 16. The device of claim 12,wherein the conductive magnetic shield element includes a magneticepoxy.
 17. The device of claim 14, wherein the plurality offerromagnetic particles are of a material having a high magneticpermeability.
 18. A method, comprising: forming a mixture of: firstferromagnetic particles of mu-metal, permalloy, elemental iron, or softiron alloy, each ferromagnetic particle including an insulating coatingof polyethylene, styrene-acrylic polymer, carboxylated styrene-butadienepolymer, dielectric oxide, silicon dioxide or ceramic material and apolymeric matrix material at a volume ratio of first ferromagneticparticles to mixture that imparts a selected magnetic permeability tothe mixture; and positioning the mixture around and between a pluralityof electrical connectors that electrically couple contact terminals of asemiconductor die with contact terminals of an input/output interface;and positioning, on the semiconductor die, a magnetic epoxy including aplurality of second ferromagnetic particles, wherein the magnetic epoxyhas a higher conductivity than the mixture based on conduction betweenthe second ferromagnetic particles.
 19. The method of claim 18, furthercomprising positioning a first shield plate coupled to the magneticepoxy.
 20. The method of claim 19, further comprising positioning asecond shield plate coupled to the magnetic epoxy.